Copays. The biggest concern is probably to cover the in hospital copay. Then skilled nursing, cancer, ambulance.....
For most folks, the most common claims are outpatient (Part B) . . . they can also be the most expensive.
Folks worry to much about a hospital stay . . . they should be more concerned about long recovery medical bills (PT, chemo, radiation, etc.) than hospital inpatient. Outpatient care really adds up. Ask a sick person if you don't believe me.